Studies on the renal transport and metabolism of choline have been performed using the renal portal circulation in hens and are currently being pursued using the isolated perfused rat kidney. The main renal metabolites of choline are betaine and phosphatidylcholine and the rates of their formation at various choline levels are being investigated along with the effect of ethanol on the renal disposition of choline. Another metabolic route has been demonstrated for the kidney by the in vivo N-oxidation of trimethylamine to trimethylamine N-oxide in the chicken. The capacity of this enzyme system is being further explored using the isolated perfused rat kidney. Preliminary data indicate that the kidney approaches the liver in its ability to form N-oxides. Measurement of plasma choline levels in uremic patients undergoing dialysis treatment showed their plasma choline levels to be significantly higher than normal. Continuing studies will explore a possible relationship between the development of uremia and plasma choline levels. Since the kidney removes from the blood a large amount of choline, renal impairment may lead to the development of high plasma choline levels. The ability of the kidney to form choline from radioactive precursors is another line of investigation. Choline synthesis by rat and chicken kidney will studied and compared. BIBLIOGRAPHIC REFERENCES: Acara, M. and B. Rennick. The biphasic effect of organic cations on the excretion of other organic cations. J. Pharmacol. Exp. Ther. 1976 (in press). Rennick, B., M. Acara and M. Glor. Renal tubular transport of choline and tetraethylammonium: relations of Tm and competition. J. Pharmacol. Exp. Ther. 1976 (in press).